This is an investigation of the effects of chronic moderate undernutrition on the social, emotional, and cognitive development of children. Six- to eight-year-old children identified as having a history of malnutrition (protein-calorie deficiency) are compared with children who have had more nearly adequate diets. These children are from villages which participated in a longitudinal study from which there are extensive data on food intake, health, growth, and earlier cognitive development. Groups are of very similar social backgrounds. Anthropometry and health and nutritional history are used to assess nutritional status. Standard tests and observations in controlled and natural settings are used in investigating cognitive, sensorimotor, and attentional capacities, and social and emotional behavior. In addition, data are obtained on the children's performance in school, and on the family and village circumstances in which the children live.